Air-heater cupola constructions



March 22, 1966 Filed Dec. 11, 1963 1. PENTEK 3,241,823

AIR-HEATER GUPOLA CONSTRUCTIONS 2 Sheets-Sheet 1 INVENTOR. A n/47v PL A Mk March 22, 1966 I. PENTEEK 3,241,823

AIR-HEATER CUPOLA CONSTRUCTIONS Filed Dec. 11, 1963 2 Sheets-Sheet 2 INVEN TOR. l'srm'm PE/WEK (WW/MW) United States Patent 3,241,823 AER-HEATER CUPOLA CONSTRUCTIONS Istvan Pentelr, Budapest, Hungary, assignor, by mesne assignments, to Licencia Talalmanyokat Ertekesito Vallalat, Budapest V, Hungary Filed Dec. 11, 1963, Ser. No. 329,647 9 Claims. (Cl. 263-19) This invention relates to air-heater cupola constructions and to a method of operation of such air heater.

As is known, combustion air for blast furnaces is preheated in air heaters. Generally, such air heaters have a cylindrical inner space or chamber with an arch roof or arched dome and refractory walls. Well known are the Cowper air-heater systems which are subdivided into a furnace shaft and a heat exchange grid shaft. In one period of operation, blast furnace or top gas is burned in the furnace shaft. The combustion products are compelled by chimney or stack draft to traverse a grid made of fire clay and thereby to partake in a heat exchange or rather heat said grid, the delivered heat being substantially stored up in the fire clay grid. In a second operational period, burning is interrupted and fresh air is supplied and blown through the heat storing grid in an opposite direction. Such fresh amounts of air pick up the heat stored in the fire clay grid and are withdrawn or discharged from the air heater at a temperature of about 800 degrees centigrade.

Where blast furnaces are operated with injected mineral oil or chamber gases, it is indispensable to increase the temperature of the hot air supplied by the air heaters from 800 degrees centigrade to a temperature of about 1000 to 1200 degrees Centigrade. However, employing blast furnace or top gases with a heat content or colorifie value of 950 calories per normal cubic meter, the temperature cannot be increased. On the other hand, gases of higher calorific values must not be burned in the usual air heaters such as the air heaters of the Cowper system because their cupola constructions cannot withstand elevated flame temperatures. For instance, flames of elevated temperature increase the air-heater cupola chamber temperatures to values which are higher than the softening point of the usual and available best fire clay bricks. Furthermore, the smoke of the blast furnace or top gases enters into a chemical reaction with the fire clay material of the cupola whereby the fire clay bricks are caused to erode and thin.

It has been suggested to dispense with the furnace shaft and to fill up the whole chamber of the air heater with a grid or lattice work for heat exchange whereby the dimensions of an air heater could be decreased for the same output. In such air heaters, the fuel is burned by means of downwardly directed burners which are disposed in the arch roof or arched dome rather than in the furnace shaft. For this purpose the cupola of the air heater had to be provided with three vaults enclosing a pair of chambers, one chamber having blast furnace or top gas and the other one having combustion air supplied to it. The injection of blast furnace or top gas was carried out through nozzles which extend across the air chamber. All conduits and armatures are connected at the level of the fuel and air chambers to the air heater which lies at the level of the cupola vault at a height of about 30 meters. However, vertical expansion of the air heater, cumbersome manipulation of the extensive overhead conduits and armatures, the impossibility of controlling heating and combustion processes as well as an increased danger of explosion considerably restricted the use of such top firings through the cupola chamber to which Cowper system air heaters have generaly been preferred where a reliable operation of blast furnaces was required.

3,241,823 Patented Mar. 22, 1966 The principal object of the present invention is a further refinement of otherwise conventional cylindrical air heaters either constructed according to the Cowper system or provided with other cupola constructions. Such development contemplates cooling of the cupola vault by means of a top level supply of additional combustion air for the burning of gases the calorific or heat value of which is higher than that of blast furnace or top gases. Also, such development is directed to combustion air being preheated to temperatures of 1200 to 1300 degrees centigrade.

Such operation is obtained by a cupola construction comprising--in accordance with a principal feature of the present invention-an inner cupola and an outer cupola separated from one another by an intermediate chamber, said cupolas closing a furnace shaft and a heat exchange grid shaft at their upper extremities, air conduits communicating with said intermediate chamber traversing said outer cupola, and a plurality of passages in said inner cupola connecting said intermediate chamber with a combustion chamber above said furnace shaft and said heat exchange grid shaft.

Further objects and details of the present invention will be described with reference to the drawings which show, by way of example, two embodiments of the invention, and in which:

FIG. 1 is a vertical sectional view of the first embodiment;

FIG. 2 is a perspective view of an embodiment of a profile brick;

FIG. 3 is a sectional view similar to that of FIG. 1 of a second embodiment; and

FIGS. 4 to 6 are horizontal sectional views along lines 4-4, 55, and 6-6, respectively, of FIG. 3.

Similar reference characters refer to similar details throughout the drawings.

FIG. 1 shows a cylindrical tower-like air heater constructed substantially according to the Cowper system and having refractory walls 1. The chamber of the air heater is subdivided by a partition 2 into a furnace shaft 3 and a heat exchange shaft 4 with fire clay grid work. A pipe conduit and gas burner 5 serve for the supply of heating gases and combustion air, respectively, whereas a pipe conduit 6 supplies blast air, and a pipe conduit 7 is provided for the withdrawal of combustion gases.

According to the invention, the furnace shaft 3 and the heat exchange shaft 4 are connected with one another by a combustion chamber 21. The cylindrical chamber of the air heater is closed by an inner cupola 8 consisting of vault elements or bricks 9 shown in FIG. 2 which are assembled in the manner of a hemisphere. As is shown in FIG. 2, the vault bricks 9 are shaped as truncated pyramids and are provided each with a groove 13. Such grooves may be provided on two or more sides of the profile brick so that each pair of such juxtaposed bricks encloses a channel. It is also possible to provide the profile brick with traversing pipe-like passages (not shown). Thus, a vault with, as it were, perforations will be obtained which has a net-like array of uniform passages. The wall it is provided with a mantle (not shown) having supports 10 fixed to it which support an outer cupola 12. The outer cupola l2 and the inner cupola 8 enclose an intermediate chamber 11.

The outer cupola 12 is built up of solid bricks. Four pipes 14 connect a circular conduit 15 with the intermediate chamber 11 provided between cupolas 8 and 12.

The pipes 14 serve for introducing air into the intermediate chamber 11 during the period of firing and blasting. Such combustion air flows from chamber 11 through the passages provided by the grooves 13 of the vault bricks 9 of the inner cupola and becomes distributed over the inner vault surface. The inner cupola 8 is cooled by the introduced fresh combustion air and protected against possible fire losses and collapsing. The amount of the additionally introduced air may be adjusted during heating andblasting, respectively, by means of valves 17 and 18 in the conduits 16 and 6, respectively, within wide limits. Moreover, it is possible to adjust the excess air amount in heating the air whereby controlling the firing, restricting the period of heating up the air heater and increasing its output are rendered possible as well. During heating and blasting the valves 17 and 18 are alternately closed. Only one group of valves can be opened when the other group of valves is closed. For this purpose, there is an interlock between valves 17 and 18.

As has been mentioned, a portion of the injected air can be introduced above the inner cupola or vault 8. Thus, blast air supply of constant temperature is obtained in the air heater. The relation between air blast and combustion air is adjusted by butterfly valves 19 and 20 in conduits 6 and 5, respectively.

Constructionally, both the perforated inner cupola 8 and the solid outer cupola 12 form self-supporting bodies. Thus, existing air heaters can be converted into apparatus according to the invention at low cost.

Obviously, by means of the invention, it is possible to suitably cool the inner cupola 8, more particularly, its surface facing the combustion chamber 21 and to protect it against overheating since about 4000 or more cooling passages may be formed by the vault bricks 9 with their grooves 13. The air traversing such cooling passages will be uniformly distributed and caused to form a continuous cooling layer at the inward side of the vault 8. Thereby, it is possible to employ gases such as natural gas, mineral gas and their mixtures, and to burn them in the furnace shaft 3 although their calorific or heat value is higher than 1000 calories per normal cubic meter, that is, exceeds the calorific or heat value of blast furnace or top gases. Moreover, the presence of the cooling layer formed by the uniformly distributed additional air permits a complete combustion of injected fuel.

With regard to heating air of elevated temperature supplied by the air heater according to the invention, it is also possible to inject augmented quantities of fuels of higher calorific or heat value such as natural gas or oil in blast furnaces and to increase the percentage amount of sintered mixtures.

FIGS. 3 to 6 show air heaters of cross-sectional areas other than circular (FIGS. 4 and and with a furnace shaft 3a separated from the gridded heat exchange shaft 4:: (FIG. 6). While in the previous embodiment both cupolas 8a and 12a were hemispherical, the cupolas of the second embodiment have a pair of lateral quarter spheres which are connected with one another by a half cylinder. Partitions 22 subdivide the intermediate chamber 11a into three partial chambers. Thus, the distribution of fresh air introduced into the combustion chamber 21a and, thereby, the uniformity of the cooling action is considerably enhanced. For keeping constant the temperature of the air blast, a portion of the air is supplied via conduit 23 forming a continuation of conduit 16a, conduit 16a and pipes 14a in the outer cupola 12a into the intermediate chamber between the cupolas 8a and 12a.

The combustion products of the quality fuel burned in the separately disposed furnace shaft 3a flow through the combustion chamber 214: below the inner cupola 8a into the gridded heat exchange shaft 4:: and therefrom through gas exhausters 24 in a funnel or chimney of the air heater (not shown).

During the period of heating, the cooling air flows from conduit 16a through control valves 25 in conduits 14a into the intermediate chamber 11a. The air amount can be adjusted by valve 26 and a control valve 25 in conduits 16a and 14a, respectively.

While injection takes place, valve 26 is closed and valve 28 in pipe conduit 23 (for adjusting the air blast) is opened. A valve 29 having been opened, the blast air flows from a circular conduit 30 at the bottom portion of the air heater into a lower part of the heat exchange shaft 4 below the grid work thereof. The traversing air blast is heated up on the grid work, and after opening a valve 32 in a conduit 31, arrives in a hot air conduit 32. The cold air, the amount of which is adjusted by valve 28 in pipe conduit 23, flows also during injection through the passages of the inner cupola 8a into the combustion chamber 21a. Adjustment of a constant hot air temperature is carried out in the air heater proper.

A heavy duty burner 33 with subdivided flame serves for burning the fuel in the furnace shaft 3a.

From the foregoing it will be appreciated that the present invention provides a cupola construction that enables the apparatus to be operated with high quality fuel of high caloric content.

Having described my invention, I claim:

1. A furnace construction for an air heater for burning quality fuels, said air heater having a furnace shaft and a heat exchange grid shaft and means separating said shafts from each other, comprising an inner top wall closing and connecting upper ends of said shafts and forming a combustion chamber disposed at least principally above said shafts, an outer top wall spaced from the inner top wall to provide an intermediate chamber, said outer top wall having air supply passages communicating with said intermediate chamber for supplying air thereto, and said inner top wall having a plurality of downwardly extending passages therein for the flow of air from the intermediate chamber to the combustion chamber.

2. A furnace construction according to claim 1, wherein the inner wall is formed of a plurality of bricks each of which is formed to provide at least one of said plurality of passages.

3. A furnace construction according to claim 1, wherein both said walls are hemispherical.

4. A furnace construction according to claim 3, wherein said inner wall is formed of pyramid-shaped profile bricks which are provided with at least one longitudinal groove on their side surfaces.

5. A furnace construction according to claim 1, wherein both said walls consist of a pair of lateral quarter spheres connected with one another by a half cylinder.

6. A furnace construction according to claim 5, wherein said intermediate chamber is subdivided by partitions provided between said inner and outer walls.

7. A furnace construction according to claim 1, wherein valve means are provided to control the flow of air into said intermediate chamber.

8. A furnace construction according to claim 1, in which said passages have a length substantially greater than their width.

9. A furnace construction according to claim 1, in which said walls are both of brick.

References Cited by the Examiner UNITED STATES PATENTS 1,068,424 7/1913 Gorman 26319 2,259,913 10/1941 Walters 26351 2,335,877 12/1943 ONealetal 263-49 3,082,995 12/1960 Krapf 263-19 WILLIAM F. ODEA, Primary Examiner.

JOHN J. CAMBY, Examiner.

D. A. TAMBURRO, Assisamt Examiner. 

1. A FURNACE CONSTRUCTION FOR AN AIR HEATER FOR BURNING QUALITY FUELS, SAID AIR HEATER HAVING A FURNACE SHAFT AND A HEAT EXCHANGE FRID SHAFT AND MEANS SEPARATING SAID SHAFTS FROM EACH OTHER, COMPRISING AN INNER TOP WALLL CLOSING AND CONNECTING UPPER ENDS OF SAID SHAFTS AND FORMING A COMBUSTION CHAMBER DISPOSED AT LEAST PRINCIPALLY ABOVE SAID SHAFTS, AN OUTER TOP WALL SPACED FROM THE INNER TOP WALL TO PROVIDE AN INTERMEDIATE CHAMBER, SAID OUTER TOP WALL HAVING AIR SUPPLY PASSAGES COMMUNICATING WITH SAID INTERMEDIATE CHAMBER FOR SUPPLYING AIR THERETO, AND SAID INNER TOP WALL HAVING A PLURALITY OF DOWNWARDLY EXTENDING PASSAGES THEREIN FOR THE FLOW OF AIR FROM THE INTERMEDIATE CHAMBER TO THE COMBUSTION CHAMBER. 